This study will examine the impact of modern treatments for metastatic Castrate Resistant Prostate Cancer (mCRPC) on several relevant 'geriatric' domains such as daily function, objective physical function, and falls. Additionally, the investigators study whether frailty is associated with worse outcomes, and whether it is possible to predict the risk of severe chemotherapy toxicity in older men.

Our primary aims are (a) to examine the impact of pre-treatment frailty on 'elder-relevant' outcomes including daily function, objective physical function, falls, quality of life (QOL), and early treatment discontinuation; (b) to determine whether the Hurria/Cancer and Aging Research Group (CARG) tool is able to predict severe (grade 3+) chemotherapy toxicity in men starting chemotherapy. Our secondary aim is to understand the impact of abiraterone and enzalutamide on 'elder-relevant' outcomes.

This is a prospective multicentre observational study. The investigators will enroll men age 65 or older with mCRPC who are starting (a) first-line chemotherapy; (b) abiraterone; or (c) enzalutamide. Assessments will occur prior to starting treatment and every 2 months thereafter until the end of treatment.

As treatment options become more complex in older men with mCRPC, understanding and predicting a wide range of treatment toxicities is important and will aid decision-making and management.

Inclusion Criteria:

1. At least 65 years of age
2. Diagnosed with prostate cancer with evidence of clinical and/or radiographic evidence of progression despite adequate androgen deprivation therapy and achievement of castration (total testosterone level <1.7 nmol/L measured within 6 months of enrollment)
3. Among men starting either abiraterone or enzalutamide, no prior chemotherapy/abiraterone/enzalutamide. Among men starting first-line chemotherapy, commencing docetaxel but can have had either prior abiraterone or enzalutamide

Exclusion Criteria:

1. Unable to speak English fluently.
2. Severe neuropsychiatric abnormalities that prevent study participation.
3. Limited life expectancy (<3 months) as estimated by the primary oncologist.

Men 65 and older starting first line chemotherapy, or Abiraterone, or Enzalutamide for mCRPC